In recent years, a vehicle has been increased in size and a demand for vans has been increased. Some types of the vans include three-row seats in a vehicle compartment. The three-row seats include first row seats, second row seats, and third row seats. Generally, the first row seats correspond to a driver's seat and a front passenger's seat. The second row seats correspond to seats arranged behind the first row seats. The third row seats correspond to rearmost seats.
When there is a great number of occupants, the third row seats can be used as a sitting space. For the purpose of ensuring a greater luggage space at a rear of the vehicle compartment, the third row seats are folded down. A known technology which uses the third row seats as the sitting space and the luggage space is disclosed in JP2008-207636A (hereinafter referred to as Patent reference 1).
A vehicle seat disclosed in Patent reference 1 includes a seat cushion serving as a seat portion in a state where an occupant occupies the seat, and a seatback serving as a seatback portion in a state where the occupant occupies the seat. The vehicle seat is retained at a usable position when the occupant occupies the seat, and is retained at a stored position when intending to ensure the volume of the vehicle compartment. In the usable position, the seat cushion is retained at a position where the occupant enables to seat thereon and the seatback is retained at an upright position in which the seatback supports a back of the occupant. On the other hand, in the stored position, the seat cushion is retained at the stored position which is positioned at a rear-bottom of the usable position of the seat cushion. In the stored position, the seatback is retained at a forwardly folded position at which the seatback is arranged at a forward of the seat cushion moved to the stored position so that the seatback and the seat cushion are arranged one in front of the other.
Generally, a headrest, which protects a head of the occupant who seats on the seat from a load applied in a rearward direction of the vehicle, is provided at a top portion of the seatback of the vehicle seat. In a case of changing positional states of the seat cushion, the seatback, and the headrest from the seatable states to the stored states, it is convenient to change the positional states automatically using a motor. In general, the motor is provided at each of the seat cushion and the seatback so that the seat cushion and the seatback are operated individually. Further, the positional states of the headrest may be changed to the stored state by folding the headrest relative to the seatback upon a detection of the movement of the seat cushion to a predetermined position. The detection of the movement of the seat cushion to the predetermined position may be realized using an operational lever provided on a moving path of the seat cushion. That is, when moving the seat cushion to the stored position, the seat cushion activates the operational lever, thus to move the headrest to the stored position thereof.
Further, in a case where automatically changing the positional states of the seat cushion and the seatback, it is preferable to include an entrapment detector in order to prevent an object, or a part of occupant's body from being trapped between the seat cushion and the seatback. The entrapment detector judges whether the object or the part of occupant's body is entrapped based on results of comparison between a detected load and a predetermined threshold for the judgment. Considering the above case that the headrest is moved to the stored position in cooperation with the movement of the seat cushion, the load which is generated when the seat cushion activates the operational lever may be mistakenly judged as a load generated by entrapping the object or the part of occupant's body. Further, the load which the seatback receives when the headrest is folded to the seatback may be mistakenly judged as a load generated by entrapping the object or the part of occupant's body.
JPH05-96371U (hereinafter referred to as Patent reference 2) discloses a system which detects an entrapment of an object or a part of occupant's body at a windowpane of a vehicle. The system for a power window disclosed in Patent reference 2 detects the entrapment of the object or the part of occupant's body between the windowpane and a sash based on an opening or closing state of the window of the vehicle.
According to the system disclosed in Patent reference 2, a detected region is divided into five regions in accordance with the opening or closing state of the window. Reference values of the absolute speed and a relative speed of a motor, which serves as a judgment reference for detecting the entrapment of the object or the part of occupant's body are determined for each of the detected regions divided into five. In a case where the system disclosed in Patent reference 2 is applied to a seat state changing apparatus which changes seat states, high performance arithmetic processing unit is required because a complex control is required, which increases a manufacturing cost. If a low performance arithmetic processing unit is applied, the seat state changing apparatus to which the system disclosed in Patent reference 2 is applied may erroneously detect the entrapment of the object or the part of occupant's body.
A need thus exists for a seat state changing apparatus which is not susceptible to the drawback mentioned above.